This invention relates generally to ram air turbines of the type used on an aircraft to drive backup electric and/or hydraulic power systems. More specifically, this invention relates to an improved ram air turbine having a secondary speed control governor for regulating turbine blade pitch angle in a manner achieving faster turbine acceleration on deployment.
Ram air turbines are generally known in the aerospace industry for use in driving auxiliary power systems in the event of a primary system failure. The ram air turbine is commonly stored within the wing or fuselage of an aircraft for deployment into the air stream when needed. The turbine includes two or more turbine blades adapted to be driven by the air stream, to provide a rotary output which can be used to drive an electrical generator and/or a hydraulic pump. Such ram air turbines are commonly equipped with a speed control governor for altering turbine blade pitch angle to achieve a substantially constant turbine rotational speed despite variations in air speed and/or load.
Since the ram air turbine is a key part of an emergency backup power system for the aircraft, turbine deployment normally does not occur unless and until a primary power system failure is encountered. When such failure occurs, it is extremely desirable for the ram air turbine to be deployed and accelerated to operational speed as quickly as possible. In this regard, speed control governors for regulating turbine speed after initial acceleration can be incompatible with optimizing turbine speed run-up upon initial turbine deployment. That is, speed control governors for ram air turbines generally function by setting the blade pitch angle in the at-rest condition at an angle which does not achieve the desired optimized rapid acceleration from the at-rest condition to the design operating speed.
The present invention provides an improved ram air turbine for use in an aircraft environment, wherein the ram air turbine includes a primary governor for speed control during normal operating conditions, in combination with a secondary governor which sets the turbine blade pitch angle in the at-rest condition for substantially optimized and rapid turbine acceleration on initial deployment.